The present invention relates to bearings, and particularly relates to a bearing configuration for reducing noise therein. The invention is useful in gear sets for electric power steering systems.
Noise in gear sets is generally undesirable, and particularly undesirable in certain applications, such as in electric power steering systems where the noise is felt at the handwheel and/or heard in the passenger compartment. Prior attempts at controlling noise in such systems have focused on reducing backlash between the teeth of a pair of gears and on dampening the noise. For example of such approaches, see U.S. Pat. No. 6,164,407, issued Dec. 26, 2000 to Cheng; U.S. Pat. No. 6,269,709, issued Aug. 7, 2001 to Sangret, and the article entitled, “Electric Power Steering” by Yuji Kozaki et al., published in 1999 in the journal, Motion & Control, issue 6, the latter of which is incorporated herein by reference in its entirety.
Although the methods used heretofore to reduce noise and the deleterious effects thereof significantly improve the performance of the gear set, they have not addressed a significant contributor to noise: the bearings. Tolerance and clearance in the roller or ball bearings supporting a shaft allows the shaft to move axially slightly, which introduces noise into the system. Traditional means for reducing bearing noise is not effective in some applications, such as in systems encountering high axial loads. In such systems, the bearings contribute noise despite axially pre-loading the bearing when a great enough axial force is exerted in the opposite direction against the pre-load. Reduction of bearing noise by radial expansion of the inner race to remove the clearance in the bearing is too expensive. The prior art has therefore not adequately addressed this source of noise.